This invention relates to valves and, more particularly, to a novel and highly effective valve for controlling the flow of a fluid under pressure.
Valves are among the most critical elements of many mechanical systems. For example, the jet engines in commercial, business and military aircraft depend on valves for controlling the flow of jet fuel reliably and without pressure surges or spikes during start-up, operation and shutdown.
Reliability is one of the most important desiderata in aircraft engines. For a number of reasons, including their rotating as opposed to reciprocating movement, the jet engines used in modern commercial, business and military aircraft are generally very reliable as compared to reciprocating engines. An engine is no more reliable, however, than the system that supplies fuel to it.
A fuel system must ensure the delivery of fuel to the engine under closely controlled pressure during start-up and operation, immediate cutoff of fuel during engine shutdown, and avoidance of surges or pressure spikes at all times.
The last requirement presents a particular challenge. Normal operating pressure of a jet engine fuel system is, say, 54 pounds per square inch. Abrupt shutoff of fuel under such high pressure tends to produce a sudden, steep pressure surge or spike. In order to fly efficiently, airplanes and their components, including fuel lines, tanks and valves, must be as light as possible, and hence tend to be fragile and subject to rupture by excessive pressure spikes. Jet fuel is highly flammable, and ignition of jet fuel flowing from a rupture in the fuel system is extremely hazardous.
Because of the importance of the problem, a great deal of attention has been given to the design of light, simple, reliable valves for use in jet engine fuel systems and other environments where the control of fluid flow is of critical importance. The best prior example of such a valve known to the applicants is the MK 81181-1 valve produced by the assignee of the present invention. This prior valve comprises a poppet valve member that can be moved between two seats and normally engages one of the seats. Behind the second seat is a spring-biased relief valve normally biased to the closed position. When fuel in the system reaches a certain "crack" pressure, it forces open the spring-biased relief valve and flows to the jet engine. Shutoff is achieved by energizing the poppet valve, which then moves away from the first seat and engages the second, thus blocking flow to the engine but permitting recirculating flow through the first seat and preventing a pressure surge.
While the prior structure provides many benefits, it has more parts and greater weight than one would ideally desire in a valve used in the fuel system of an aircraft engine.